EP1482328B1 - Apparatus to read-out information stored in a phosphor layer - Google Patents

Abstract

Device for capturing information contained within a phosphor layer comprises a light source (10) for transmission of stimulation light (12) which is incident on a stimulation line (16) of the phosphor layer and is suitable for exciting emissive light within the phosphor layer, a detector for detecting the emissive light and a elongated hollow mirror (14) for focussing the light from the light sources on the phosphor layer. In so doing the light from the light source is magnified by a factor of 1 to M, where M is between 0.5 and 2.

Description

The invention relates to a device for detecting information contained in a phosphor layer according to the preamble of claim 1.

Generic devices are used, in particular for medical purposes, in the field of computer radiography (CR) (see the document US Pat. No. 4,829,180). In this case, X-ray images are recorded in a phosphor layer by storing the X-ray radiation passing through an object, for example a patient, as a latent image in the phosphor layer. To read the latent image, the phosphor layer is irradiated with stimulation light and thereby excited to emit emission light, which corresponds to the latent image stored in the phosphor layer. The emission light is detected by an optical detector and converted into electrical signals, which further processed as needed, displayed on a monitor or to a corresponding output device, such. A printer.

Devices are known from the prior art in which the stimulation light emitted by a light source strikes a linear area the phosphor layer is focused by means of cylindrical lenses. In such devices, the stimulation line, to which the stimulation light emanating from the light source is focused, can not usually be arbitrarily sharply defined. For a high image quality of the image to be read, however, the sharpest possible limitation of the stimulation line is required.

It is an object of the invention to provide a device for detecting information contained in a phosphor layer, in which the highest possible image quality is ensured.

This object is achieved according to claim 1 by an elongated, in particular cylindrical, concave mirror for focusing the stimulation light emitted by the light source onto the phosphor layer, wherein the light source is imaged onto the phosphor layer on a scale of 1: M and M has a value between about 0, 5 and 2 adopts.

The use of an oblong concave mirror greatly reduces aberrations that lead to a blurred image of the light source on the phosphor layer compared to cylindrical lenses. In particular, aberrations due to spherical aberration are thereby completely eliminated and aberrations due to astigmatism and coma are greatly reduced. This strong reduction of aberrations is inventively achieved in that the magnification, d. H. the ratio of image size to object size assumes a value between 2: 1 (M = 0.5, magnification) and 1: 2 (M = 2, reduction). The invention achieves a high degree of sharpness in the imaging of the light source onto the phosphor layer, so that a high quality of the image read out from the phosphor layer is ensured.

Preferably, the light source is imaged onto the phosphor layer on a scale of 1: 1. At this scale aberrations are particularly low and thus the picture quality is particularly high.

In a further embodiment, it is provided that the light source extends parallel to the stimulation line. As a result, an even greater sharpness of the stimulation line is achieved in a simple manner.

Advantageously, the concave mirror is arranged parallel to the stimulation line. As a result, the sharpness of the image can be further increased in a simple manner.

In a further preferred embodiment of the invention it is provided that the concave mirror is designed as a cylindrical mirror, which has the shape of a circular arc in cross section. In alternative variants of this embodiment, the cylindrical mirror has the shape of an elliptical arc or an aspherical profile in cross section. In all the above-mentioned cross-sectional shapes of the cylinder mirror, a sharper image of the light source onto the phosphor layer and thus higher image quality is achieved compared to correspondingly shaped cylindrical lenses.

In a further embodiment it is provided that the optical axis in the cross section of the concave mirror, which in particular has a circular arc-shaped cross section, intersects the concave mirror in a vertex and the light source is tilted by a tilt angle about the vertex against the optical axis of the concave mirror. By tilting the radiation sources against the optical axis of the concave mirror, the stimulation line, on which the stimulation light emanating from the light source is focused, is also tilted in the opposite direction against the optical axis of the concave mirror. By an appropriate choice of the tilt angle thus the distance of the light source from the stimulation line can be adapted to constructive requirements.

The distance d of the light source and / or the stimulation line from the vertex of the concave mirror of the relationship d = R cos ² ω, where R denotes the radius of curvature of the concave mirror and ω denotes the tilt angle, preferably satisfies the cross section of the concave mirror. By astigmatism and coma conditional aberrations, which with increasing tilt angle ω increase, can be kept very small in this way, so that a high image sharpness and thus image quality is guaranteed.

A further embodiment of the invention provides that the detector has a plurality of detector elements arranged parallel to the stimulation line. This allows a spatially resolved detection of emanating from the stimulation line emission light.

In one embodiment of the device, the light source comprises a plurality of individual radiation sources arranged along a line, each of which emits stimulation light bundles, which are focused by the concave mirror onto the stimulation line and at least partially overlap on the stimulation line. By superimposing the individual stimulation light bundles in the direction of the stimulation line, a high intensity of the stimulation light is achieved with simultaneously low intensity fluctuations along the stimulation line.

A further embodiment of the invention provides that the light source is designed as a line light source, which is designed to emit stimulation light along a continuous line. As a result, intensity fluctuations are kept very low.

In an alternative embodiment, it is provided that the light source comprises a radiation source and a deflection device, wherein the stimulation light emitted by the radiation source is periodically deflected by the deflection device and focused by the concave mirror on a focus area on the phosphor layer, that the focus area, the phosphor layer along the Periodically sweeps stimulation line. Even with such systems, aberrations that would lead to a blurring and widening of the focus area and thus to a reduction in image quality are significantly reduced by the invention.

Fig. 1

ein erstes Ausführungsbeispiel der Erfindung in Seitenansicht;

Fig. 2

das in Fig. 1 dargestellte erste Ausführungsbeispiel in Draufsicht;

Fig. 3

ein zweites Ausführungsbeispiel der Erfindung; und

Fig. 4

ein drittes Ausführungsbeispiel der Erfindung.

The invention will be explained in more detail with reference to figures. Show it:

Fig. 1

a first embodiment of the invention in side view;

Fig. 2

the first embodiment shown in Figure 1 in plan view.

Fig. 3

a second embodiment of the invention; and

Fig. 4

a third embodiment of the invention.

Fig. 1 shows a first embodiment of the invention in side view. A light source 10 emits stimulation light 12 in the form of a divergent in the plane of stimulation light beam 13, which is reflected at an elongated concave mirror 14 which is perpendicular to the plane of the figure, and thereby focused on a likewise perpendicular to the plane of the figure stimulation line 16.

The light source 10 in this example comprises individual radiation sources 11, which are arranged along a line. This is illustrated in Fig. 2, which shows the first embodiment shown in Fig. 1 in plan view. The radiation sources 11 of the light source 10 arranged along a straight line emit stimulation light 12, which also has the form of divergent stimulation light bundles 15 in the plane of FIG. 2. The divergent in the plane of Fig. 2 stimulation light beam 15 of the individual radiation sources 11 are reflected on the concave mirror 14 and superimposed on the stimulation line 16. As can be seen in Fig. 2, the individual radiation sources 11 and the elongated concave mirror 14 are parallel to the stimulation line 16 arranged. The stimulation line 16 lies on a phosphor layer (not shown) from which a latent image stored therein is to be read out.

In this embodiment, the elongated concave mirror 14 is formed as a cylindrical mirror whose cross section has the shape of a circular arc. Such cylinder mirrors are inexpensive to produce and result in the described devices to a strong reduction of aberrations.

The cross section of the cylinder mirror can also be an aspherical, d. H. have a course deviating from the shape of a circular arc, by which intensity, sharpness and width variations along the stimulation line 16 can be additionally reduced. In particular, the cylindrical mirror may have a cross section in the form of an elliptical arc. Such a shaped cylindrical mirror has two focal lines, wherein the light source 10 is arranged in a first focal line and the stimulation line 16 extends along a second focal line. In this case, an aberration-free focusing of the stimulation light 12, and thus a very sharp limitation of the stimulation line 16, is achieved for any imaging scales. The cylindrical mirror may also have the shape of a parabolic arc in cross section. This is advantageous, for example, when the stimulation light 12 emitted by the light source 10 has the form of a parallel light beam or a light beam with only a very small divergence.

In the example shown, the elongated concave mirror 14 has straight generatrices which run perpendicular to the plane of FIG. For the purposes of the invention, however, the elongated concave mirror 14 may also have a shape in which the generatrices are curved. In this way, a further degree of freedom in the design of the shape of the concave mirror 14 and thus in the reduction of aberrations, for example, due to additional optical components in the beam path of the stimulation light beam 13 is obtained.

As shown in FIG. 1, the light source 10 and the stimulation line 16 are each tilted by a tilt angle ω against the optical axis 5 of the concave mirror 14. The tilting takes place here about the vertex S, in which the optical axis 5 of the concave mirror 14 intersects this. By choosing the tilt angle ω, the distance between the light source 10 and the stimulation line 16 to constructive requirements, such. As a specific lighting and / or detection geometry can be adjusted.

By using an elongated concave mirror 14 for focusing the divergent stimulation light bundles emanating from the individual radiation sources 11 13 is obtained a much sharper limited and more homogeneous in its width stimulation line 16 than is achieved in the known from the prior art focusing of the stimulation light 12 by means of cylindrical lenses. This can be explained by the fact that, when focusing the individual stimulation light bundles 13 of the radiation sources 11 by means of cylindrical lenses, aberrations occur due to a curvature of the individual focus lines, also called Focusbow, along the stimulation line 16, which results in a sharpness variation and consequently a width variation of the line to lead. By using an oblong concave mirror, these aberrations are eliminated or at least greatly reduced, so that a width variation of the stimulation line 16 in the line direction is avoided or reduced. Thus, even with a composite of a plurality of individual radiation sources 11 light source 10 is a uniformly wide and thereby sharply limited stimulation line 16 obtained on the phosphor layer.

In the first exemplary embodiment illustrated in FIGS. 1 and 2, the light source 10 is imaged onto the stimulation line 16 on a scale of 1: 1. The scale here refers to an image or focusing in the plane of FIG. 1. By this one-to-one imaging, aberrations that result in particular in a blurring of the image of the light source 10 on the stimulation line 16 are greatly reduced. In particular, this avoids aberrations due to spherical aberration. However, the sharp limitation of the stimulation line 16 required for a high image quality is achieved not only at a reproduction scale of 1: 1, but also at scales between 1: 2 and 2: 1. With imaging scales deviating from 1: 1, within the range between 1 : Although 2 and 2: 1 show aberrations due to spherical aberration, astigmatism and coma, surprisingly, they are so small that nevertheless a very high image quality can be guaranteed.

To keep aberrations due to astigmatism and coma particularly low, the distance of the light source 10 and / or the stimulation line 16 is selected by the concave mirror 14 in dependence of the selected tilt angle ω. Especially the distance d of the individual radiation sources 11 and / or the stimulation line 16 from the vertex S of the concave mirror 14 of the equation d = R cos ² ω, which is related to the respective optical axis 5 in cross section of the concave mirror 14, is sufficient where R denotes the radius of curvature of the concave mirror. In the case of the concave mirror 14, which has a circular arc-shaped cross-section in the example of FIG. 1 as a cylindrical mirror, the radius of curvature R corresponds to the distance of the circular arc to the center P of this circle.

In the first exemplary embodiment of FIGS. 1 and 2, the light source 10 comprises a plurality of radiation sources 11 arranged along a straight line. Alternatively, the light source 10 can also be designed as a line light source which emits the stimulation light 12 along a continuous line. In contrast to a light source 10 composed of a plurality of individual radiation sources 11, there are no longer any width fluctuations along the stimulation line 16. Abnormalities due to spherical aberration and / or astigmatism are greatly reduced by the inventive use of an elongated, in particular cylindrical, concave mirror, so that a significantly increased sharpness of the stimulation line is achieved.

In a further alternative embodiment, the light source 10 has only one radiation source 11, the stimulation light bundle 13 emanating from the radiation source 11 being periodically deflected by a deflection device and focused by the elongated concave mirror 14 onto a point-shaped or linear focus area on the phosphor layer 21. Due to the periodic deflection of the stimulation light bundle 13, the focus area sweeps over the phosphor layer along the stimulation line 16. The respective excited emission light is detected by a detector. Devices of this type are also referred to as flying spot systems. Even with such systems, aberrations that would lead to a blurring and widening of the focus area and thus to a reduction in image quality are significantly reduced by the invention.

3 shows a second exemplary embodiment of the invention, in which the divergent stimulation light beams 13 emitted by the light source 10 are first reflected on an oblong plane mirror 18 before they strike the oblong concave mirror 14 and from there along the stimulation line 16 onto the phosphor layer 21, which is mechanically stabilized by a carrier layer 23, are focused. By using the plane mirror 18 are compared to the first embodiment shown in FIG. 1 additional possibilities in the spatial arrangement of the light source 10, the concave mirror 14 and the phosphor layer 21 obtained, allowing an adaptation of the device according to the invention to design requirements, without additional aberrations cause.

Instead of the plane mirror 18, a suitable optical prism for deflecting the stimulation light bundle 13 can also be used. It is also possible to use an elongated convex mirror or another elongated concave mirror for deflecting the stimulation light bundle 13.

The spatial arrangement of the light source 10, the concave mirror 14 and the stimulation line 16 extending on the phosphor layer 21 relative to one another take place in this example analogously to the first exemplary embodiment shown in FIGS. 1 and 2. In particular, the light source 10 and the plane mirror 18 are arranged so that the light source 10 is also tilted by a - in this case virtual - tilt angle ω against the optical axis 5 of the concave mirror 14. The distances of the light source 10 and the phosphor layer 21 from the vertex S of the concave mirror 14 are also selected so that a 1: 1 image-related to the plane of Figure 3 - takes place and thus aberrations are reduced to a minimum.

The emission light 17 excited along the stimulation line 16 in the phosphor layer 21 is imaged onto the detector 25 by means of imaging optics 24. The detector 25 is designed as a linear detector which has a multiplicity of individual detector elements arranged parallel to the stimulation line 16. Parallel to the linear detector 25, the imaging optics 24, which preferably as a linear microlens or Gradientenindexlinsen array, in particular Selfoclinsen array is formed.

When the latent image stored in the phosphor layer 21 is read out, the device combined to form a reading unit 30 is moved in a transport direction T over the phosphor layer 21, which is successively excited and read out along the stimulation line 16. As an alternative or in addition to the movement of the reading unit 30, the phosphor layer 21 located on the carrier layer 23 can also be moved relative to the reading unit 30.

Fig. 4 shows a third embodiment of the invention, which has a particularly compact construction. The cross-section of the concave mirror 14 is oriented substantially perpendicular to the phosphor layer 21 in this example, whereby the distance of the light source 10 from the phosphor layer 21 can be reduced. The outgoing from the light source 10 divergent stimulation light beam 13 meet in this example directly on the concave mirror 14 and are focused by this on the stimulation line 16, wherein in the beam path between the concave mirror 14 and the phosphor layer 21, a plane mirror 18 is inserted, which is the of Concave mirror 14 reflects reflected and now convergent light beam on the stimulation line 16. As in this embodiment, the plane mirror 18 opens a variety of ways to arrange the light source 10, the concave mirror 14 and the phosphor layer 21 relative to each other, whereby in particular a very compact arrangement of the individual components can be achieved.

4, the phosphor layer 21 to be read is located on a carrier layer 23, which is permeable to the stimulation light, so that the phosphor layer 21 can be excited from its underside. In the illustrated case, the emission light 17 is imaged by an imaging optical system 24 onto a detector 25 from the upper side. Alternatively, however, the emission light 17 can also be detected by the transparent carrier layer 23 from the underside. With regard to the imaging optics 24 and the detector 25, the statements on the one shown in FIG. 3 apply second embodiment accordingly. Also for the inventive choice of the elongated concave mirror 14, the inclination angle ω and the magnification of the explanations apply to the embodiments described in Figures 1 to 3 accordingly.

Claims (14)

1. Device for detecting information which is contained in a phosphorus layer, comprising a light source (10) for emitting stimulation light (12), incident upon the phosphorus layer (21) along a stimulation line (16) and suitable for stimulating emission light (7) in the phosphorus layer (21), a detector (25) for detecting the emission light (17) which is stimulated in the phosphorus layer (21), and an elongated concave mirror (14) for focusing the stimulation light (12) emitted by the light source (10) onto the phosphorus layer (21), characterised in that the light source (10) is projected onto the phosphorus layer (21) at a scale of 1:M and M takes a value between 0.5 and 2.
2. Device according to claim 1, characterised in that the light source (10) is projected onto the phosphorus layer (21) at the scale of 1:1.
3. Device according to any one of the preceding claims, characterised in that the light source extends (10) parallel to the stimulation line (16).
4. Device according to any one of the preceding claims, characterised in that the concave mirror (14) is arranged parallel to the stimulation line (16).
5. Device according to any one of the preceding claims, characterised in that the concave mirror (14) is in the form of a cylinder mirror, which in cross-section has the form of a circular arc.
6. Device according any one of claims 1 to 4, characterised in that the concave mirror (14) is in the form of a cylinder mirror, the cross-section of which is aspherical.
7. Device according to claim 6, characterised in that the concave mirror (14) is in the form of a cylinder mirror, which in cross-section has the form of an arc of an ellipse or parabola.
8. Device according to any one of claims 5 to 7, characterised in that the optical axis (5) in the cross-section of the concave mirror (14) intersects the concave mirror in a vertex (S), and the light source (10) is tilted by a tilt angle (ω) around the vertex (S) relative to the optical axis (5) of the concave minor (14).
9. Device according to claim 8, characterised in that the distance (d), along the optical axis (5) in the cross-section of the concave mirror (14), of the light source (10) and/or the stimulation line (16) from the vertex (S), satisfies the relationship d = R cos²ω, where R designates the radius of curvature of the concave mirror (14).
10. Device according to any one of the preceding claims, characterised in that the detector (25) has a plurality of detector elements which are arranged parallel to the stimulation line (16).
11. Device according to any one of the preceding claims, characterised in that the light source (10) comprises a plurality of individual radiation sources (11) which are arranged along a line.
12. Device according to claim 11, characterised in that the individual radiation sources (11) each emit stimulation light bundles (13), which are focused by the concave mirror (14) onto the stimulation line (16) and are at least partially superimposed on the stimulation line (16).
13. Device according to any one of claims 1 to 10, characterised in that the light source (10) is in the form of a linear light source, which is in a form for emitting stimulation light (12) along a continuous line.
14. Device according to any one of claims 1 to 10, characterised in that the light source (10) includes a radiation source and a deflection device, wherein the stimulation light (12) which the radiation source emits is periodically deflected by the deflection device and focused by the concave mirror (14) onto a focal region on the phosphorus layer (21), in such a way that the focal region spreads periodically over the phosphorus layer (21) along the stimulation line (16).

Images